Whether it's harmful or not depends on the lifespan of the garment and whether or not that "natural" garment replaces enough throw-away garments to make it wort

Whether it's harmful or not depends on the lifespan of the garment and whether or not that "natural" garment replaces enough throw-away garments to make it worthwhile. Sure, it's totally possible for a well-made synthetic garment to last as long or longer than a natural one (many of our dead uncle's double knit polyester slacks are still kicking-it in a thrift store somewhere). But we're talking here about "fast fashion", which is entirely cheaply made garments that, by definition, have a short lifespan. These are typically synthetic fabrics or cotton/polyester blends.